Integrity of stored data in magnetic media, such as magnetic tapes, disks and diskettes, is usually susceptible to the presence of noises. When distortion caused by noises is mild, the data can be restored by error correction techniques such as ECC. When the distortion is severe, however, conventional error correction techniques may not be able to restore the integrity and the stored data may become unusable.
To reduce distortion caused by noises, many conventional magnetic storage devices use a filter to remove unwanted components of the read-out signal. Unfortunately, noises experienced by magnetic storage systems have many causes. These causes include crosstalk, incomplete erasure, feed-through and misregistration. Because the characteristics of these noises are so different, it is usually impossible to cost-effectively eliminate their effects by a simple filter system.
To make matter worse, a device may often have to read data from media which were written by other devices, including devices that are made by different manufacturers using different components and designs. The use of different components and designs further increases the differences of noises and reduces the effectiveness of the filter.
To enable a device to operate with the maximum number of media, the filter in many conventional devices is set to an "compromise level", which is estimated to allow the filter to eliminate noises commonly found in most devices. Unfortunately, while this level may accommodate most devices, it may in some circumstances aggravate the distortion such as by reducing components needed to reproduce the data signal. As a result, the compromise level may sometimes increase the read errors or media errors.